328 



PLANT STUDIES 



gated, and is usually covered by a delicate flap {inr/iixiiiiii) 

 wliieli arises from the epidermis (Fig. 290). Occasionally 

 the sori are extended along the under surface of the mar- 

 gin of the leaf, as in maidenhair fern [Adiaiil iiiii)^ and the 

 common brake (I'lerix), i\i which case they are pi'otected 

 l)y the inrolled margin (Fig. 398), which may be called a 

 " false intlusium." 



It is evident that such leaves are doing two distinct 

 kinds of work — chlorophyll work and spore formation. 

 This is true of most of the ordinary Ferns, hut some of 



them show a tendency to divide 

 the work. Certain leaves, or 

 certain leaf-branches, produce 

 spores and do no chlorophyll 

 work, while others do chloro- 

 phyll work and produce no 

 S2)ores. This differentiation in 

 the leaves or leaf-regions is in- 

 dicated by a2i2)roi)riate names. 

 'J'hose leaves which produce 

 only spoi'cs are called sjjoro- 

 pJiylls, meaning " spore leaves,'' 

 while the leaf branches thus 

 set apart are called sporophyll 

 branches. Those leaves whidi 

 only do cldoroi)hyll work are 

 called foJidfje lea res ; and such 

 branches are foliage branches. 

 As sporo]>hylls are not called 

 u]ion for chlorophyll work they 

 often liecome much modifii'd, being much more compact, 

 and not at all resembling the foliage leaves. Such a differ- 

 entiation may be seen in the ostrich fern and sensitive 

 fern (O/iiifh'ii) (Fig. '.'DOI, the climbing fern { Li/r/nfliinn), 

 the royal fern {Oxmii luhi), the nioonwort {/Idfri/fln'inii) 

 (Kig. 300), and the adder's tongue {()/i/ii(i(/I(ixsinii). 



Fro. 398. T.cnflcts nf two roTmnnn 

 fi^rns : .1, the common bi'ake 

 iPlfvU): Tt. maif]PTib:lir {Adiaii- 

 finn)\ botli piinwinLT ^'ori liornr' 

 at the inarL'iii and prolrrtr.l liy 

 the infold. 'd iiiaTL'in. wlii.h thus 

 forms a false indnsiinii. - Cald- 

 well. 



